iFITS

iFITS is a free, open-source app for viewing and analysing 2D images and 3D data cubes in the FITS format, on iPad and iPhone.

iFITS screenshot

Quick start

1. Open a FITS file

Tap Open File at the top left and choose a .fits file. You can also:

In the Files app, touch and hold a FITS file, then choose Open With › iFITS.
Drag a FITS file onto the iFITS window.

Pinch to zoom and drag to move around. Tap ↺ to reset the view. Tap or hover over a pixel to see its value and sky position in Pixel Info.

The four modes

The V A R S buttons on the left switch between the four modes. The orange one is the mode you’re in.

2. Change how the image looks (V)

In V (Visualization) mode, the Render Configuration panel at the bottom controls the image:

Colormap: inferno, viridis, gray and more. Turn on Invert colormap to flip it.
Scaling: Linear, Log, Square Root, Squared, Gamma or Power.
Clip: pick a percentile, or drag the red lines on the histogram.

3. Annotate (A)

In A (Annotation) mode, draw on the image with Apple Pencil. Use the toolbar to pick a color, turn finger drawing on, hide your notes or clear them. Annotations are saved inside the FITS file.

4. Draw regions and get statistics (R and S)

In R (Regions) mode, pick a shape (ellipse, rectangle, line or point) and drag on the image, or tap for a default size. Tap a region to edit its name, color and position. Use Import / Export Regions (.reg) to share regions with DS9.

In S (Statistics) mode, see the statistics of the selected region or of the entire image.

5. Read the FITS header

Tap H in the toolbar to see every header keyword and value. On iPad, choose File › Show Header in New Window (⌥⌘H) to keep it open beside the image.

6. Step through a data cube

When the file is a cube, the cube button in the toolbar turns on. Tap it to open the Animator: play the channels, step one at a time, or drag the slider. You can also change the frame rate.

7. See a spectrum

For a spectral cube, tap the spectrum button (the line chart) in the toolbar. Hover over or double-tap a pixel to see its spectrum. To get the spectrum of a whole area, draw a region in R mode, then pick it in the spectrum panel and choose the statistic, such as the mean. You can overplot several spectra. Drag the orange line to change channel.

8. View the cube in 3D

Tap the AR button in the toolbar. Drag to rotate, pinch to zoom, twist to roll and double-tap to reset. The options button changes the opacity, value range and depth.

9. Place the cube in your room (AR)

In the 3D view, tap Place the cube in the room. Move your device slowly, then tap a table or the floor. Pinch to resize the cube and drag to turn it. iFITS asks for camera access the first time. It only uses the camera live, and never records.

10. Open spectra in their own window

On iPad, tap the open-in-new-window button in the spectrum panel to show the spectra in a separate window beside the image.

Saving: annotations and regions are saved into your FITS file automatically. To save only when you choose, turn off Autosave in ••• › Settings and press ⌘S.
Share: the share button sends the FITS file. Choose Export and Send… to send a PNG or JPEG of the image as you see it.

Keyboard shortcuts

Shortcut	Action
⌘O	Open a FITS file
⌘S	Save
⌘1, ⌘2, ⌘3, ⌘4	V, A, R and S modes
⌘= and ⌘−	Zoom in and out
⌘0	Reset view
⇧⌘G	Show or hide the coordinate grid

Need help?

See Support, or open an issue on GitHub.